Traditionally, the incandescent is used as a light source for an omni-directional light. The major disadvantages of that type of light are low efficiency and short life span. Since 1990s, LEDs have been used as light source in many applications. The common incandescent lamp provides an illumination pattern in all directions. It is this standard that must be met if LEDs are to replace it in the applications. Early LEDs were limited to about a 30-degree viewing angle. Today, it is common for LEDs to provide a 120-degree illumination pattern but the intensity is still reduced to 50% at the extremes of the pattern.
There are various ways to extend the illumination pattern of LEDs. One of the common methods is diffusion, using a diffraction-style lens or canopy. The disadvantage of these methods is that they may attenuate the total light output and fail to provide an even intensity light pattern in all directions. Another method is to mount many LEDs, pointing in all directions, in a framework similar to a pine cone. This approach is costly and difficult to manufacture. It also provides bright spots where the LEDs are located.
Various LED based omni-directional lights have been developed. In U.S. Pat. No. 5,594,433, Terlep disclosed an omni-directional LED lamp in three embodiments. In the first embodiment, two LEDs are mounted side by side in a miniature bayonet base that can fit into a conventional miniature bayonet socket. The side-by-side LEDs face semi-spherical mirror reflectors that distribute the unidirectional light emitted from the LEDs over an omni-direction. A second embodiment has two LEDs facing one another with a spherical mirror reflector between to cause unidirectional light to be omni-directional. In a third embodiment, a semi-spherical reflector is mounted in the top of a lens cover above an LED. The components are housed in a sealable casing for marine applications where the casing can be mounted to a dock piling.
In U.S. Pat. No. 6,086,220, Lash, et al, disclosed a marine safety light including a LED array which consists of a plurality of LEDs arranged in a star configuration. The LED array preferably consists of six white LEDs evenly spaced in the horizontal plane and positioned within a fresnel lens such that an even omni-directional distribution of light is emitted. The LED array is powered using a power circuit which includes two conventional DC to DC converters which regulate the output voltage, allowing the marine light to operate at a constant brightness for a substantial period of time on a conventional 1.5 volt power source.
In U.S. Pat. No. 6,533,446, Chen, et al, disclosed a light using LED as light source. A light guide receives and guides light output from the light source. The light guide extends out from the light source. A reflector is positioned in the light guide and reflects the light guided through the light guide to provide the appropriate illumination.
In U.S. Pat. No. 6,568,834, Scianna disclosed a light modifying material composed of ethylene/butene-1 copolymer or propylene homopolymer or a combination of the two, and lighting devices using the material in a light transmitting cover. The light source for the devices is a semiconductor or LED, to produce an energy efficient light source.
In U.S. Pat. No. 7,021,801, Mohacsi disclosed a high-intensity light comprising a side-emitting optoelectronic device adapted to emit light of a desired color. A heat sink is positioned adjacent the optoelectronic device and a reflector at least partially surrounds the optoelectronic device. The reflector is spaced a distance from the optoelectronic device. A window portion is sized to output the light in a desired arc.
In U.S. Pat. No. 7,261,454, K. Y. Ng disclosed an omni-directional LED device. In one embodiment, an opaque barrier is created and in some embodiments enhancement surfaces are created below the opaque barrier to increase lumen output from the device sides. In one embodiment, a reflecting structure is created to assist with horizontal light mixing. The horizontally mixed light is then redirected through a structure, such as an LED structure, to create a high lumen output, slender back-lighted display.
In U.S. Pat. No. 7,378,983, Wang, et al, disclosed a LED signaling apparatus for navigational aids. The signaling apparatus comprises a plurality of high intensity LEDs with their output beams individually controlled by high precision optical beam transformers. The transformed LED beams are mixed in a predetermined manner by controlling the relative position, angular orientation, and other parameters of the LEDs to produce a desired illumination pattern.
However, all these systems or apparatuses suffer from complex structure, leading to low reliability, difficulty in assembly, high light transmission loss, and low operational efficiency.
What is desired is an improved omni-directional light system which offers a combination of simple structure, long life time, low cost, high luminous power, compact size, and high reliability.